This invention relates generally to data processing, and more particularly to a method and system for quantizing an input signal.
Communications systems often use analog-to-digital converters to sample analog input signals. The analog signals may contain information that will be processed by the communications system. Typically, the analog-to-digital converter receives the analog signal, samples the analog signal at different times, and generates digital representations of the analog signal at those times. A processor or other computing device in the communications system uses the digital representations of the analog signal to approximate the analog signal.
Many types and styles of analog-to-digital converters have been developed. Analog-to-digital converters often use a latch to quantize an analog input signal and generate a digital output signal. To quantize the analog input signal, the latch typically remains in a first state until the analog input signal exceeds a minimum threshold. While in the first state, the latch generates a low digital output signal. When the analog input signal exceeds the minimum threshold, the latch switches to a second state. In the second state, the latch generates a high digital output signal.
One type of analog-to-digital converter uses transistors to form the latch. A problem with this type of converter is that the operating speed of the converter is typically low. Signals in the converter typically must travel through the various transistors in the circuit. The path that the signals traverse is typically long. As a result, these longer distances slow the operating speed of the analog-to-digital converter. The analog-to-digital converter is unable to sample the analog input signal at higher sampling rates.
Another type of analog-to-digital converter uses a current sink and a tunneling diode as the quantizer. The tunneling diode typically operates in two states, one corresponding to a high digital output and one corresponding to a low digital output. In this type of quantizer, the tunneling diode is typically reset before each sample is taken of the analog input signal. This helps to ensure that the tunneling diode provides an accurate digital representation of the analog input signal during each sample of the analog signal. For example, the tunneling diode may be reset to generate a low digital output before each sample.
The tunneling diode is usually reset by a circuit that receives a reset signal. A problem with prior approaches is that prior analog-to-digital converters often use slow reset circuits. The slow speed of the reset circuit causes the tunneling diode to be reset at a slower speed. This slows the operating speed of the analog-to-digital converter and prevents the converter from sampling the analog input signal at higher sampling rates.
The present invention recognizes a need for an improved method and system for quantizing an input signal. The present invention reduces or eliminates at least some of the shortcomings of prior systems and methods.
In one embodiment of the invention, a system for quantizing an input signal having a time-varying voltage includes a voltage-to-current converter operable to convert the input signal to a proportional current. The system also includes a first negative differential resistance element coupled in series with the voltage-to-current converter. The first negative differential resistance element is operable to switch from a first state to a second state based on the proportional current. In addition, the system includes a reset circuit coupled in parallel with the first negative differential resistance element. The reset circuit includes a second negative differential resistance element, and the reset circuit is operable to reset the first negative differential resistance element to the first state based on a reset signal.
In another embodiment of the invention, a method for quantizing an input signal having a time-varying voltage includes converting the input signal to a proportional current, providing the proportional current to a first negative differential resistance element, and sampling the input signal based on the proportional current using the first negative differential resistance element. The first negative differential resistance element is operable to switch from a first state to a second state based on the proportional current. The method also includes resetting the first negative differential resistance element to the first state based on a reset signal using a reset circuit. The reset circuit includes a second negative differential resistance element coupled in parallel with the first negative differential resistance element.
In yet another embodiment of the invention, a system for quantizing an input signal having a time-varying voltage includes a voltage-to-current converter comprising a current source. The voltage-to-current converter is operable to convert the input signal to a proportional current. The system also includes a negative differential resistance element coupled in series with the voltage-to-current converter. The negative differential resistance element is operable to switch from a first state to a second state based on the proportional current. The system further includes a reset circuit coupled in parallel with the negative differential resistance element. The reset circuit is operable to reset the negative differential resistance element to the first state based on a reset signal.
Numerous technical advantages can be gained through various embodiments of the invention. Various embodiments of the invention may exhibit none, some, or all of the following advantages. For example, in one embodiment of the invention, a system is provided that quickly quantizes a time-varying input signal. In a particular embodiment, the system uses a tunneling diode, such as a Resonant Tunneling Diode (RTD), to quantize the input signal. The use of a tunneling diode increases the speed of the system. The input signal is not forced to travel through long distances in the system, which helps to increase the operating speed of the system.
Another advantage of some embodiments of the invention is that a faster reset circuit may be used within the system. In a particular embodiment, the reset circuit uses a second tunneling diode to reset the first tunneling diode. The use of a second tunneling diode to reset the first tunneling diode increases the speed of the reset circuit. Because the reset circuit operates at a higher rate, the system may also operate at a higher rate. This allows the system to sample the input signal at higher sampling rates.
In addition, some embodiments of the invention use a current source instead of a current sink. The current source may allow the system to sample the input signal at a faster rate. This also increases the operating speed of the system and allows the system to sample the input signal at higher sampling rates.
Other technical advantages are readily apparent to one of skill in the art from the attached figures, description, and claims.